Atmospheric sampling devices

ABSTRACT

An atmosphere sampling chamber is disposed within a container. The chamber has an inlet communicating with the atmosphere to be sampled and an outlet communicating with an analysis device such as a gas chromatograph. The annulus in the container adjacent the outer walls of the chamber contains a fluid medium for pressurizing the chamber to exhaust its contents through the outlet. In one embodiment, the chamber is a gas-impervious bellows which is exhausted by feeding gas to the container. In another embodiment, the chamber is formed of a hydrogen-permeable palladium alloy tube and the fluid medium is an electrolyte capable of transporting an ionic species of hydrogen. When the tube is electrolytically connected to a counter electrode in a first evacuation polarity mode, the tube is exhausted and, sample is charged into the tube. In the reverse polarity mode, hydrogen is generated through the tube wall and acts as a purging gas and carrier gas to discharge the sample and sweep the sample through the gas chromatograph column and detector.

United States Patent Low et al.

[ 1 May 16, 1972 [54] ATMOSPHERIC SAMPLING DEVICES [72] Inventors: George M. Low, Deputy Administrator of the National Aeronautics and Space Administration with respect to an invention of; James E. Lovelock, Bowerchalke, near Salisbury, Wiltshire, England; Peter G. Simmonds, 5200 Palm Drive, La Canada, Calif. 9101 l 22 Filed: Oct. 15,1970

21 Appl.No.: 81,095

Primary Examiner-S. Clement Swisher AttorneyJ. H. Warden, Paul F. McCaul and John R. Manning [57] ABSTRACT An atmosphere sampling chamber is disposed within a c0ntainer. The chamber has an inlet communicating with the atmosphere to be sampled and an outlet communicating with an analysis device such as a gas chromatograph. The annulus in the container adjacent the outer walls of the chamber contains a fluid medium for pressurizing the chamber to exhaust its contents through the outlet. In one embodiment, the chamber is a gas-impervious bellows which is exhausted by feeding gas to the container. In another embodiment, the chamber is formed of a hydrogen-permeable palladium alloy tube and the fluid medium is an electrolyte capable of transporting an ionic species of hydrogen. When the tube is electrolytically connected to a counter electrode in a first evacuation polarity mode, the tube is exhausted and, sample is charged into the tube. In the reverse polarity mode, hydrogen is generated through the tube wall and acts as a purging gas and carrier gas to discharge the sample and sweep the sample through the gas chromatograph column and detector.

10 Claims, 5 Drawing Figures P'A'TE'N'TEDMM 16 I972 3.662.604

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INVENTORS.

JA E. LOVELOCK BY PE G.SIMMONDS /z z/z ATTORNEYS.

ATMOSPHERIC SAMPLING DEVICES ORIGIN OF THE INVENTION The invention described herein was made in the performance of work under a NASA contract and is subject to the provisions of Section 305 of the National Aeronautics and Space Act of 1958, Public Law 85-568 (72 Stat. 435; 42 USC 2457).

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to atmosphere sampling devices and systems including means for charging the device with sample and discharging the sample to form a carrier gas dispersion suitable for analysis.

2. Description of the Prior Art In many scientific and industrial situations, the ambient pressure of the environment to be sensed or monitored is very low and it is difficult to collect an adequate volume of uncontaminated sample. Furthermore, in terrestrial applications it is inconvenient to be required to collect samples in containers and to deliver the containers to an analytical station where the sample is removed, processed and analyzed. In planetary exploration, the collection removal and analysis must be conducted on board the space vehicle and the data telemetered to earth.

SUMMARY OF THE INVENTION The sampling devices of the invention are simple and reliable mechanisms capable of operating in diverse environments and includes means for charging a sampling chamber and means for discharging the chamber to the inlet to an analysis system. The sampling device includes a container in which is disposed a sample receiving chamber. The chamber has a valved inlet for exposure to the atmosphere during a charging cycle and a valved outlet in open communication with the analysis system during the discharging cycle. The container is connected to a source of fluid medium and actuating means for discharging the chamber during the discharging cycle.

These and many other attendant advantages of the invention will become better understood by reference to the following detailed description when considered in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic view of a first embodiment of an atmospheric sampling device according to the invention incorporating a bellows sampling chamber;

FIG. 2 is a schematic view of a further embodiment of a bellows sampling device utilizing a single source of carrier on propellant gas to compress the bellows and to propel the gas into the analytical equipment;

FIG. 3 is a schematic view of a sampling device including a tubular carrier gas permeable electrode immersed in an electrolyte capable of associating with generating the carrier gas;

FIG. 4 is a schematic view of a further embodiment of an electrolytic charging and discharging sampling device; and

FIG. Sis a sectional view through line 5-5 ofFIG. 4.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to FIG. 1, the sampling device 10, generally includes a container 12, a pressuring system 14 for the container and a gas impermeable, compressible closed end bellows 16, mounted within the container. The interior 18 of the bellows 16 forms the sample receiving chamber. The open end 20 of the bellows is connected to a T-shaped fitting 22.

The side branch 24 of the fitting 22 communicates with the atmosphere to be collected when valve 26 is in open position. The vertical branch 28 of the fitting 22 communicates with conduit 32 when valve 30 is open. One end of the conduit 32 is connected to a source 36 of sweep gas through a regulating valve 38. The propellant or sweep gas is a very pure inert gas such as nitrogen or. may be a carrier gas such as hydrogen or helium when the analysis device is a GC. The other end of conduit 32 is connected to an analysis device, not shown.

The pressuring system 14 for exhausting or discharging the bellows includes a pressured container 40 such as a CO, cylinder, a quick release valve 42 and actuating means therefor such as a squib 44. The control signal for the squib 44 may be supplied by a telemetering receiver unit 46.

To set the device 10 for charging, the bellows I6 and the annular chamber 50 within the container 12 surrounding the bellows 16 are evacuated completely. This ensures that the chamber 18 is not contaminated and presets the bellows for collection by contracting it as shown in solid line in the drawing. Valves 26, 30 and 42 are then closed and the squib and CO cylinder 40 is attached to the container 12. In the case of planetary exploration, only chamber 50 need be evacuated before flight. Valve 26 is left open or opened during flight. The vacuum of space will exhaust the contents of bellows chamber 18. Valve 26 may then be left open or closed and reopened during descent, collect gas from the planetary atmosphere within the bellows chamber 18. The bellows 16 then expands to the position shown in broken line in the drawing. After the sample is collected, valve 26 is closed.

The device is discharged by opening regulating valve 38 to flow sweep gas from source 36 past the branch 28. Valve 30 is opened the squib actuator 44 is actuated by unit 46 to puncture the diaphragm valve 42. CO from cartridge 40 enters the annular chamber 50 and compresses bellows 16 to inject the collected sample into the gas stream flowing in conduit 32. The dispersion of sample in propellant or carrier gases is swept into the analysis device, suitably a gas chromatographic column and detector. The squib operated device is only capable of collecting and discharging a single sample of gas. It would be desirable to be able to cyclically charge and discharge the unit.

The sampling device illustrated in FIG. 2 utilizes the propellant gas to effect contraction of the bellows and is capable of repeated operation to obtain many samples depending upon the supply of propellant gas. The bellows 16 is fabricated with rather stiff convolusions which require appreciable pressure to effect compression of the bellows. The bellows 16 is again disposed in an outer container 12 and the open end 20 of the bellows is connected to a fitting 22 having a first side branch 24 communicating with atmosphere through valve 26 and a vertical branch 28 communicating with conduit 32 through valve 30.

In this embodiment, the squib operated actuator 14 is eliminated and discharge pressure is provided by a by-pass conduit 60 which communicates with annular chamber 50 and with conduit 32 on the inlet side thereof adjacent the propellant gas source 36 and regulating valve 38. An additional valve 62 is provided downstream from the by-pass conduit 60 and a flow restrictor 64 such as an orifice plate may also be included within the conduit 32 to maintain flow of the propellant or sweep gas at a prescribed rate to prevent overloading of the gas chromatograph or other detector.

To operate this device, valves 62 and 30 are opened and a source of vacuum is connected to the outlet 66 of conduit 32 to evacuate both annular chamber 50 and sampling chamber 18 within bellows l6. Valves 62 and 30 are then closed and the device is ready for charging. The device is then placed within the atmosphere to be sampled and valve 26 is opened to capture a sample within sampling chamber 18 and valve 26 is closed. Regulating valve 38 and valve 62 are opened to start a flow of carrier gas through the flow restrictor 64 towards the detector and through by-pass conduit 60 into annular chamber 50. The pressure of the carrier gas is adjusted so that the gas entering chamber 50 is not sufficient to compress bellows 16.

When the collected sample is to be injected into the analytical device, valve 62 is closed and valve 30 is opened. The carrier gas will then flow only through the by-pass conduit 60 and will gradually increase the pressure of the gas within chamber 50 and will compress the bellows l6 and inject the sample into conduit 32 through valve 30. After the bellows 16 has been compressed, valve 62 is opened and the carrier gas sweeps past vertical branch 28, mixes with the injected sample in conduit 32 and sweeps the mixture into the gas chromatograph through exit port 66. The flow restrictor 64 prevents an undesirable sudden surge of propellant gas on opening of valve 62. This cycle may be repeated continuously until the supply of carrier gas is exhausted.

A further version of a sampling device is illustrated in FIG. 3 which obviates the need of a separate vacuum source to pump down the system for charging and a separate propellant gas source to discharge the device and to supply the carrier gas for analysis. Both of these systems add weight and mechanical complication to the device. 8

A further version of an atmospheric sampling mechanism illustrated in FIG. 3 incorporates features of the novel combined carrier gas generator-separator unit described in copending application, Ser. No. 7,922, filed Feb. 2, 1970, the disclosure of which is incorporated herein by reference. The sample collecting chamber 18 in this embodiment is formed by a closed end tube 70. At least a portion of the wall of the tube 70 is formed of a material selectively permeable to carrier gas, suitably a palladium alloy in the case of hydrogen carrier gas.

The open end 72 of the tube 70 is connected to a T-shaped fitting 74 having a vertical branch 76 communicating with atmosphere through a valve 78 and a side branch 80 communicating with a detector device such as a gas chromatograph through a valve 82. The upward end of the tube 70 is inserted through an electrically insulating end plug 84 of a container 86. The end plug 84 also contains an aperture for receiving a counter electrode 87, and a second aperture receiving a pressure relief valve 88. The container is substantially filled with a body of electrolyte 90. The electrolyte is capable of transporting an ionic species of the carrier gas between the electrode tube 70 and the counter electrode 87. The electrodes 70 and 87 are connected to a source of potential 92 by means of conductors 94 through a polarity reversing switch 96.

The tube 70, counter electrode 87 and electrolyte 90 form an electrochemical cell 98 capable of generating hydrogen within chamber 18 when operated in a first polarity mode and capable of exhausting hydrogen from chamber 18 when operated in a second polarity mode. The electrochemical cell 98 thus functions as a combined generator-evacuator.

When hydrogen is utilized as the carrier gas, the tubular electrode 70 may be formed of a thin film of conductive material selectively permeable to hydrogen. Palladium and its alloys are remarkably permeable to hydrogen when heated to a temperature above about 100 to l 50 C. The film of palladium containing material is suitably maintained at temperatures below 600 C to avoid unnecessary catalytic change in the components of the sample.

Pure palladium when subject to temperatures cycling in the presence of hydrogen suffers mechanical distortion. However, an alloy of palladium containing to 30 percent silver, preferably about 25 percent silver is as permeable to hydrogen and is mechanically stable. Other palladium alloys, for example, palladium-rhodium or palladium-gold alloys may confer more resistance to corrosion to the films and extend the useful life of the generator-evacuator but are less permeable to hydrogen. The palladium tube 70 may be provided in various configurations and lengths of tubing may be connected in parallel to provide increased surface area with less flow resistance. Membranes or tubes can also be formed from a base structural material such as a porous ceramic coated with a thin film of palladium or a suitable hydrogen permeable palladium alloy.

The counter electrode 87 may be formed of a variety of conductive materials, suitably a strip of noble metal, such as platinum. The electrode 87 may also take the form of a closed tube formed of a palladium alloy. In this configuration, the hydrogen entering the electrolyte during operation in the evacuator mode enters and is stored within the electrode tube 87. This hydrogen is available for purging the sample chamber 18 during a generation mode of operation. The cell is thus operated in a more stoichiometric manner, obviating the need to add water and operates under less pressure from oxygen or hydrogen generated in the electrolyte compartment.

The electrolyte is a material capable of transporting an ionic species of the carrier gas from one electrode to the other, is inert with respect to the electrodes, is stable at temperature of operating the cell and is capable of re-generating the carrier gas by electrolytic association or dissociation as is required. The electrolyte may be an acid, a basic or salt material but is preferably an inorganic metal hydroxide.

The most suitable material for use in the generator-evacuator of the invention are the Group 1 metal hydroxides, such as sodium hydroxide, potassium hydroxide, or lithium hydroxide. The hydroxides should be utilized in hydrated form, preferably containing 10 to 35 percent water of hydration. Since this both lowers the power requirement and the temperature at which the electrolyte becomes molten, improved operation of the cell occurs when at least 10 to 25 percent of the lighter weight lithium hydroxide is mixed sodium or potassium hydroxide, preferably the latter. Commercial potassium hydroxide containing 25 percent water melts at 275 C. The addition of 10 percent lithium hydroxide to this electrolyte further lowers the temperature at which the electrolyte becomes molten to about 200 C.

To maintain the palladium containing electrode tube at a hydrogen permeable temperature, the cell may be heated by various means such as by disposing it in an oven or by heating the container 86 by means of an external electrical heating coil or some other suitable heating arrangement. Though it is desirable to maintain the resistance of the electrodes and electrolytes as low as possible, for purposes of electrical power efficiency, the electrolytic cell may in some configurations, provide a sufficient internal impedance to produce the desired heating on passage of current through the electrodes and electrolytes. Thus, the electrolysis current supplied by the power source 92 may be utilized to provide a necessary heat to maintain the electrode tube 70 at a hydrogen permeable temperature.

When the electrolytic cell 98 is connected to the potential source 92 through the polarity reversing switch 96 such that the electrode tube 70 is a cathode and the counter electrode 87 is the anode, hydrogen is generated by the decomposition of the electrolytic water in the electrolyte into oxygen and hydrogen. The generated hydrogen passes through the heated wall tube 70 and collects within the chamber 18. The pressure "will increase as long as potential is applied to a maximum of about 600 psi. Since only a small volume of hydrogen is required to operate the sampling device, the amount of oxygen concurrently generated is of reasonable volume and is not expected that the pressure will unduly over-pressure the cell structure. However, if pressure within the cell 98 rises to too high a level, provision for venting may be provided by means of a relief valve 88.

Evacuation of hydrogen from the tube 70 is effected by reversing the electrical connections to the electrodes 70 and 87 by means of polarity reversing switch 20. In this polarity mode the palladium containing tube 70 is anodic and the platinum electrode 87 is cathodic. Hydrogen gas in the chamber 18 will then pass through the heated wall of the tube 70 and will be associated by the electrolyte to form water. Injection of sample requires sacrifice of a quantity of hydrogen and venting an equivalent volume of oxygen. This loss may be compensated by replenishing the electrolyte with water from a supply of water connected to the container 86.

Evacuation of the sample collecting chamber 18 is accomplished by flushing the chamber with hydrogen for a period after injection of the collected sample by operating the electrolytic cell in the generation mode. During the flushing cycle, valve 82 leading to the gas chromatograph is closed while valve 78 leading to atmosphere is opened. After an appropriate flushing period, valve 24 is closed.

The chamber 18 then contains very pure hydrogen gas which is removed into the electrolyte by reversing the current by means of switch 96 to render the tubular electrode anodic. The hydrogen gas contained in chamber 18 will be evacuated through the heated wall of the tube as described above. The device is then ready for charging with sample.

When valve 78 is thereafter opened, the local atmosphere will be drawn into chamber 18. Valve 78 is then closed to capture the sample and the current is then applied from source 92 in a hydrogen generating mode. The generated hydrogen enters chamber 18, mixes with the sample and when valve 82 is opened, the mixture is swept through the tube into the gas chromatograph.

The initial flow of generated hydrogen may be non-linear in flow rate and the volume necessary to empty chamber 18 and sweep the mixture into the chromatograph may not be compatible with the column parameters especially in the case of a column operated in the flow programming mode. Even in the situation in which post column separation is utilized to separate the hydrogen carrier gas before introduction of the sample to the chromatographic detector or to a mass spectrometer, the initial flow rate from the sampling chamber to the detector may affect the operation of the column and therefore, provide anomalous responses in the detector or the mass spectrometer. The sampling device illustrated in FIGS. 4 and 5 includes a carrier gas collection chamber of controlled volume disposed intermediate the electrolytic carrier gas generationevacuation cell and the sample collection chamber.

The sampling device 100 is formed from a tubular member 102 having an outlet 104 communicating with the analysis device, not shown, through a valve 106 and a branched inlet 107 communicating with the atmosphere to be sampled through a valve 108. The tube 102 is formed of a gas and liquid impermeable material and the portion forming the electrolytic cell 110 is suitably formed of electrically insulating material. The tube 102 and the end plug 112 can be formed of a synthetic organic resin or plastic, suitably a polytetrafluoroethylene, such as Teflon.

The tube is divided into an electrolytic cell 110, a carrier gas collection chamber 114 and a sample collection chamber 116. The electrolyte compartment 118 is formed between the end plug 112 and an electrode film 120 inserted across the circumference of the tube 102. The film 120 is suitably formed of a metal selectively permeable to carrier gas, which again may be a palladium alloy, such as a 75% palladium-25% silver alloy in the case of hydrogen carrier gas. The carrier gas collection chamber 114 is disposed between the electrode film 120 and a second film 122, which is also inserted across the total circumference of the tube 102. The film 122 is also formed of a material which is selectively permeable to carrier gas in a first state of actuation and is substantially impermeable to carrier gas in a second state. The film may again be formed ofa palladium alloy in the case of hydrogen carrier gas and the actuation may be accomplished by various means of heating the film 122. The sample collection chamber 116 is defined between the film 122 and the valves 106 and 108.

A counter electrode 124 has a first portion inserted through plug 112 into electrolyte chamber 118, and a second end extending outwardly therefrom which is connected to power source 126 through conductor 128.

As shown in FIG. 5, electrode disc films 120 and 122 each have a connector tab 130 extending from the surface of tube 102. The film 120 is connected to the power source 126 through a polarity reversing switch 132 and the electrode film 122 is connected to the power source through a switch 134.

In order to prepare the device for charging the sample collection chamber 116 must be evacuated. This can be effected by connection of a vacuum source to either inlet 107 or outlet 104. However, since the cell 110 is again capable of generation or evacuation, the cell 110 can be operated in the hydrogen generation mode through polarity reversing switch 132. Flushing is accomplished by operating the cell 110 and the generation mode for a suitable period with the switch 134 closed such that the film 122 and film 120 is heated to hydrogen permeable temperature, and valves 106 and 103 are opened to flush hydrogen throughout the tube 102. Valves 106 and 108 are then closed and the switch 132 reversed to the evacuation mode with switch 134 closed such that the hydrogen within chamber 116 and 114 is redrawn through films 122 and and is electrically associated within the electrolyte to form water. Switches 132 and 134 are then opened.

Hydrogen collection chamber 114 and sample collection 116 are then under vacuum. A sample is then collected by placing inlet 107 within the atmosphere to be sampled and opening valve 108 to capture sample within chamber 116, and valve 108 is then closed. To inject sample, film 122 should be in its hydrogen impermeable cold mode. In this mode, the film disc 122 is inconsequently permeable to hydrogen and can function as a hydrogen valve. When it is desired to inject the sample within chamber 116 into the analytical device, switch 132 is closed in the gas generation mode and gas is generated through electrode film 120 into chamber 114. Gas generation is continued until a suitable pressure has been achieved within chamber 114. In this condition, a plug of hydrogen is contained within the chamber 114.

Under these conditions, the sample is ready for injection into the analytical device. Switch 132 is opened. The electrode disc film 120 is allowed to cool to hydrogen impermeable condition. Concurrently switch 134 is closed to heat membrane disc film 122 to its hydrogen permeable condition and valve 106 is opened. Hydrogen diffusing through film 122 will sweep the sample within chamber 116 through the outlet 104 and into the analytical device. Only a small intermixture of the sample and hydrogen will occur at the interface between the sample and the plug of hydrogen gas from chamber 114. Since a controlled amount of hydrogen is used for injection, this arrangement is very efiective in keeping the sample and hydrogen separated.

Although the sampling devices described are very suitable for sampling gas in planetary exploration, it is apparent that these devices are very useful for terrestrial purposes such as collecting gas samples for smog analysis and for other industri al and commercial chemical analysis procedures.

It is further to be realized that only preferred embodiments of the invention have been described and that numerous substitutions, alterations and modifications are permissible without departing from the spirit and scope of the invention as defined in the following claims.

What is claimed is:

l. A device for sampling an atmosphere comprising in combination:.

wall means defining a sample chamber having a sample inlet and a sample outlet, at least a portion of said chamber walls being formed of a material selectively permeable to a fluid when heated;

means for heating said wall portion to a temperature at which the wall portion becomes permeable to said fluid;

container means surrounding said chamber defining a compartment for receiving said fluid;

a source of said fluid for pressurizing the chamber to exhaust the contents thereof when said fluid is in contact with said wall and when said outlet is open; and

valve means in said inlet and outlet for selectively communicating said inlet with said atmosphere and said outlet with an analysis instrument.

2. A device according to claim 1 in which said walls form a gas-impervious, compressible and extensible bellows defining a sample chamber therein.

3. A device according to claim 2 in which said source of fluid comprises a source of high pressure gas and valve means between said source and said container for selectively feeding said gas to said compartment to compress said bellows.

4. A device according to claim 1 in which said fluid is hydrogen gas and said material comprises palladium.

5. A device according to claim 4 in which said fluid is an electrolyte capable of electrolytically associating and dissociating hydrogen and is received in said compartment in contact with said wall portion and said device further includes an electrode film received within said compartment in contact with said electrolyte, a source of potential and conductor means connecting said potential source to said electrode and said wall portion to form a hydrogen generation electrolytic cell.

6. A device according to claim further including a polarity reversing means interposed in said conductor means for operating said cell in a hydrogen evacuation mode for withdrawing the hydrogen from said chamber through said wall portion into said electrolyte.

7. A device according to claim 6 further including a hydrogen collection chamber disposed between said wall portion and said sample chamber and wherein the wall of said collection chamber facing said sample chamber includes a palladium containing film and further including means for selectively heating said film to a hydrogen permeable temperature.

8. A device according to claim 5 in which said material comprises an alloy of palladium containing -30% silver.

9. A device according to claim 9 in which said electrolyte comprises a Group I metal hydroxide containing 10-35 percent water.

10. A method of collecting a sample of an atmosphere comprising the steps of:

disposing a portion of a tubular element having an inlet and an outlet within a body of electrolyte, said element having a wall portion selectively permeable to gas when heated and said electrolyte being capable of associating and dissociating said gas;

disposing an electrode in said electrolyte;

connecting said electrode and wall portion to a potential source to generate said gas from said electrolyte through said wall portion with said inlet open to flush said element with said gas;

closing said inlet, reversing the polarity to said cell and evacuating said gas from said element through said wall portion into said electrolyte;

communicating said outlet with an analytical instrument,

opening said outlet; and

connecting said electrode and wall portion to said source in a gas generation mode to generate hydrogen through said wall portion and flush said collected sample into said instrument. 

1. A device for sampling an atmosphere comprising in combination: wall means defining a sample chamber having a sample inlet and a sample outlet, at least a portion of said chamber walls being formed of a material selectively permeable to a fluid when heated; means for heating said wall portion to a temperature at which the wall portion becomes permeable to said fluid; container means surrounding said chamber defining a compartment for receiving said fluid; a source of said fluid for pressurizing the chamber to exhaust the contents thereof when said fluid is in contact with said wall and when said outlet is open; and valve means in said inlet and outlet for selectively communicating said inlet with said atmosphere and said outlet with an analysis instrument.
 2. A device according to claim 1 in which said walls form a gas-impervious, compressible and extensible bellows defining a sample chamber therein.
 3. A device according to claim 2 in which said source of fluid comprises a source of high pressure gas and valve means between said source and said container for selectively feeding said gas to said compartment to compress said bellows.
 4. A device according to claim 1 in which said fluid is hydrogen gas and said material comprises palladium.
 5. A device according to claim 4 in which said fluid is an electrolyte capable of electrolytically associating and dissociating hydrogen and is received in said compartment in contact with said wall portion and said device further includes an electrode film received within said compartment in contact with said electrolyte, a source of potential and conductor means connecting said potential source to said electrode and said wall portion to form a hydrogen generation electrolytic cell.
 6. A device according to claim 5 further including a polarity reversing means interposed in said conductor means for operating said cell in a hydrogen evacuation mode for withdrawing the hydrogen from said chamber through said wall portion into said electrolyte.
 7. A device according to claim 6 further including a hydrogen collection chamber disposed between said wall portion and said sample chamber and wherein the wall of said collection chamber facing said sample chamber includes a palladium containing film and further including means for selectively heating said film to a hydrogen permeable temperature.
 8. A device according to claim 5 in which said material comprises an alloy of palladium containing 10-30% silver.
 9. A device according to claim 9 in which said electrolyte comprises a Group I metal hydroxide containing 10-35 percent water.
 10. A method Of collecting a sample of an atmosphere comprising the steps of: disposing a portion of a tubular element having an inlet and an outlet within a body of electrolyte, said element having a wall portion selectively permeable to gas when heated and said electrolyte being capable of associating and dissociating said gas; disposing an electrode in said electrolyte; connecting said electrode and wall portion to a potential source to generate said gas from said electrolyte through said wall portion with said inlet open to flush said element with said gas; closing said inlet, reversing the polarity to said cell and evacuating said gas from said element through said wall portion into said electrolyte; communicating said outlet with an analytical instrument, opening said outlet; and connecting said electrode and wall portion to said source in a gas generation mode to generate hydrogen through said wall portion and flush said collected sample into said instrument. 